CT Imaging Issues in the Critically Ill

1. CT Imaging Issues in theCritically Ill • E. Wiebe, MD, FRCPC • Department of Radiology • University of Alberta

2. CT Imaging Issues in theCritically Ill • I have no financial or other disclosures

3. Imaging Issues and Strategies Patient selection Region of interest Use of contrast IV contrast Use of oral contrast Contrast risk Radiation risk

4. Imaging Issues and Strategies Patient selection Clinical findings Prior imaging findings Imaging limitations and access Relative contraindications

5. Imaging Issues and Strategies Patient selection Region of interest Clinical findings Mechanism of injury Previous imaging findings

6. Imaging Issues and Strategies Noncontrast exam Acute retroperitoneal hemorrhage Bone injuries Aortic dissection or rupture IV Contrast use Vascular injuries and diseases Solid organ assessment Bowel wall assessment

11. Imaging Issues and Strategies Oral contrast use Positive contrast (eg. Telebrix or Gastrografin Demonstates bowel leak Impairs bowel wall assessment Variable lumen distention Negative contrast (eg. Water or Polyethylene glycol solution) Better assessment of bowel wall Cannot identify bowel leak

39. Imaging Issues and Strategies Contrast risk Anaphylactoid reaction Nephrotoxicity

40. Imaging Issues and Strategies Anaphylactoid reaction Dose and concentration independent Screen patients for increased risk Preventative premedication with corticosteroids and antihistamines No correlation or association with shellfish allergy and povidone-iodine skin cleansing solution

41. Imaging Issues and Strategies Nephrotoxicity recent meta-analysis suggested that the risk of contrast-induced nephrotoxicity is less than previously suggested (Radiology 2010; 256:21–28) Most recent study concludes that there is increased risk in patients with estimated GFR of <40ml/min (Radiology 2013: 268:719-28)

42. Imaging Issues and Strategies Nephrotoxicity Dose dependent Intravenous hydration is most important preventative measure Consider benefit of noncontrast scan

43. Imaging Issues and Strategies Radiation dose and risk Main concern is induction of cancer ALARA principle Recognize the relative risk of CT and radiography Use technology advances made to decrease dose

44. Imaging Issues and Strategies Radiation dose Measured as effective dose in mSV Background radiation dose: 3mSv/yr Standard CT abdomen dose: 8-10mSv for single scan Low dose exams decrease dose to 2-4mSv/scan

45. Imaging Issues and Strategies Radiation dose Dose estimate based on dose-length product (DLP) which is given with each scan Chest CT dose = 0.017 x DLP Abdomen CT dose = 0.015 x DLP Head CT dose = 0.023 x DLP Neck CT dose = 0.059 x DLP

46. Imaging Issues and Strategies 625 x 0.015 = 9.37 mSv659 x 0.015 = 9.88 mSv630 x 0.015 = 9.45 mSvTotal effective dose = 28.7 mSv

47. Imaging Issues and Strategies Total effective dose = 166 x 0.017 = 2.82 mSv

48. Imaging Issues and Strategies • Tailor exam to clinical situation • Use intravenous and oral contrast when necessary but not always • Be aware of risks of imaging

49. Questions?